Reinforced flexible tubular pipe with conveying back of leak fluid

ABSTRACT

A reinforced flexible tubular pipe including an inner liner ( 3 ) that forms a barrier against outflow of medium that flows through the pipe, the inner liner ( 3 ) being encased by at least one reinforcing layer having a space in which a number of profiles are configured that are coiled around the inner liner such that the profiles are completely or partially surrounded by a lumen ( 10 ) that allows transport of fluids in the longitudinal direction of the pipe. Outside the reinforcing layer an outer coating ( 9 ) is provided to form a barrier against inflow of fluids or gases from the surroundings of the pipe to the reinforcing layer. At least one flow path ( 11 ) is provided to convey fluid or gas away from the lumen ( 10 ). This flow path ( 11 ) is provided with an inlet opening that debouches in the lumen ( 10 ) and an outlet opening ( 13 ) that ends in the inner liner of the tubular pipe. The flow path ( 11 ) may be provided with a pump ( 12 ) or a one-way valve ( 15 ) that prevents fluid or gas from flowing into the lumen from the pipe interior.

The present invention relates to a reinforced flexible tubular pipecomprising an inner liner that forms a barrier against outflow of themedium that flows through the tubular pipe, said inner liner beingencased by at least one reinforcing layer containing a number ofprofiles that have been coiled around the inner liner in such a mannerthat the profiles are entirely or partially contained in a lumen thatallows transport of fluids in the longitudinal direction of the tubularpipe, and wherein—outside the reinforcing layer—an outer jacket isprovided with a view to forming a barrier against unimpeded inflow offluids and/or gases from the environment surrounding the tubular pipeand to the reinforcing layer. Such a reinforced flexible tubular isdisclosed in Schlimmelpfennig, “A novel flexible offshore LNG-pipesystem with continues operating control”.

The reinforcing layer is not secured to the inner liner, but is able tomove relative thereto which ensures the flexibility of the tubular pipe.Outside the reinforcing layer, an outer coating is provided with a viewto forming a barrier against inflow of fluids and/or gasses from theenvironment surrounding the tubular pipe to the reinforcing layer.

However, positioning of reinforcing elements in the outer coating makesit possible to impart to this layer a structural functionality, too.Also, outside the outer jacket, a further reinforcing layer can beprovided. To prevent collapse of the inner liner, it is often lined witha flexible steel pipe. In the following this pipe is designated‘carcass’.

Most often such tubular pipes are used to transport fluids and gases atvarious depths of sea, and they are used in particular in situationswhere very high or varying water pressures prevail along thelongitudinal axis of the pipe. Examples of such include riser pipes thatextend from the seabed and up to an installation on or near sea level.In the technical literature this type of riser pipes is known as risers.Also between installations arranged on the seabed at great depth, orbetween installations near the surface of the sea, this type of tubulardesign is employed. Pipes for this use, are known in the technicalliterature as flowlines or jumpers.

The coiled reinforcing layer of the tubular pipe is configured of anumber of layers of profiles, often of steel, mounted at like ordifferent pitches.

During manufacture, transport and operation the tubular pipe is exposedto circumferential pressure as well as forces acting along the axis ofthe tubular pipe. It is thus the task of the reinforcing layer to absorbthese forces to prevent the inner liner from being destroyed.

The specific configuration of the reinforcing layer depends on the useof the tubular pipe. It should be noted in particular in connection withthe reinforcing layer that it contains a lumen between the coiledprofiles which is necessary to enable the reinforcing profiles to moverelative to each other. The movability of the reinforcing profiles isnecessary to ensure the flexibility of the tubular pipe.

It is a problem with the known tubular pipes that a certain diffusionwill always occur through the inner liner which means that undesiredamounts of gases and condensate will accumulate in the reinforcing layeria with ensuing. corrosion of the reinforcing profiles.

Furthermore accumulation of pressure in the reinforcing layer due to gasdiffusion can cause the outer jacket to burst which will destroy thetubular member.

Several methods are known for reducing or preventing the destructiveeffect of diffusion into the reinforcing layer.

NO 300471 B1 discloses a method of ventilating the reinforcing layertowards the surroundings which is possible when a positive,super-atmospheric pressure prevails between the reinforcing layer andthe surroundings.

A similar method is also described in U.S. Pat. No 4932810. However, itshould be noted that the tubular pipe described in the US disclosure isof a different type.

WO 98/40657 A1 teaches how it is possible to construct a tubular memberof two concentric shells so as to provide therebetween a flushing space.The flushing space thus accomplished is cleaned continually by a mediumflowing therethrough.

Despite the fact that both NO 300471 B1 and WO 98/40657 A1 teach methodssuitable for ventilating or cleaning reinforcing layers, both methodsare less suitable for the maintenance of a flexible tubular member, theobject of which being to transport fluids at great varying depths ofsea.

The unsuitability of the methods is due to the fact that pipes operatingat varying depths of sea are often attacked by gases and fluids thatpenetrate the reinforcing layer with ensuing formation of condensate,said condensate accumulating at the lowermost part of the pipe. NO300471 B1 does not teach a method of removing such condensate, thevalves shown in the patent for ventilation acting exclusively on gasesthat are ventilated at a positive difference of pressure between thereinforcing layer and the environment surrounding the tubular pipe.

Nor does WO 98/40657 A1 teach a method suitable for removal ofcondensates from the reinforcing layer on tubular pipes arranged belowwater at varying depths.

This is due to the fact that tubular pipes of the kind disclosed thereinoften contain a mixture of condensate and accumulated gases with aneffective density which is substantially lower than that of water.

A forced flushing of the tubular pipe will therefore not be possiblewithout pressurising the reinforcing layer near the point of entry forthe flushing agent to a pressure that exceeds the ambient pressure.Pressurisation of the reinforcing layer, may entail a rupture of theouter jacket of the tubular pipe with ensuing destruction of the tubularpipe, bearing in mind that pressurisation of the tubular pipe with theobject of flushing same can only be accomplished in practice providedthe pressurisation occurs in the upper part of the tubular pipe.

In the light of this it is the object of the present invention toprovide a reinforced, flexible tubular pipe that completely or partiallyremedies the above-mentioned drawbacks associated with the prior artpipes.

In accordance with the present invention this is accomplished by atubular pipe of the type described in the introductory part which ischaracterised in that at least one flow path is arranged for conveyingfluids from said lumen to the fluid transported in the inner liner ofthe tubular pipe.

In this manner it is possible, at all depths of sea, to empty thereinforcing layer without substantial, adverse pressurisation. Furtheradvantageously, the surrounding environment is not exposed tocontamination by fluids that derive from the reinforcing layers.

In some cases, eg in case of transport of aggressive fluids, theconditions of operation can be such that the flow path isadvantageously, and as featured in claim 2, configured with means thatprevent flow into the lumen of the fluid which is transported in thepipe interior.

Convenient embodiments of these means can be configured such, asfeatured in claim 3, that the means consist of a valve that allows flowonly in case there is a negative difference in pressure between the pipeinterior and the lumen.

In case the pressure within the pipe only rarely drops below thepressure in the reinforcing layers, the means can conveniently beconfigured in accordance with claim 4, ie in the form of a pump thatforces the flow from the lumen and to the pipe interior, and furthermorethe pump can, as featured in claim 5, be configured with a passageway ora bypass valve thereby enabling flow at any time provided there is anegative difference of pressure between the pipe interior and the lumen.

In this context it should be noted that use of a pump is particularlyadvantageous, the partial pressure (which is desirably low-value) of egaggressive fluids in the free volume being hereby controllable,irrespective of the pressure within the inner liner of the pipe.

In an alternative embodiment there is, as featured in claim 6, provideda safety valve in the flow path. This safety valve can be used tooptionally close the flow path completely to flow of fluid or gas, ifdesired.

Conveniently, as featured in claim 7, two or more blocking valves areprovided that are, flow-wise, arranged on each their side of the meansarranged in the flow path. Hereby the advantage is obtained that in casedefaults occur in the valve or pump configured in the flow path withensuing operational shutdowns, such failure can be remedied withoutresulting exposure of neither the lumen nor the pipe interior to thesurroundings.

Moreover, the reinforced flexible tubular pipe can conveniently, and asfeatured in claim 8, comprise a coupling element for attachment of thereinforced flexible tubular member on another construction or to anothertubular pipe where the flow path extends completely or partially intothe coupling element.

In this manner, it can be completely or partially avoided to perforatethe liner and the coating and optionally the reinforcing layer itself.

Moreover, in practice the reinforced flexible tubular pipe can, asdescribed more detailed in claim 9, comprise at least two reinforcedflexible tubular pipes, said tubular pipes being connected in extensionof each other by means of connecting elements, and wherein theconnecting element is provided with passages that allow fluid and gas inthe one reinforced flexible tubular member to flow through the couplingelement to the reinforcing layer in the second of the two reinforcedflexible tubular pipes.

A further, preferred embodiment of the reinforced, flexible tubular pipeis, as featured in claim 10, additionally provided with at least onefurther flow path with a view to introducing to the reinforcing layerfluids or gases for cleaning and maintenance. Such cleaning fluids canbe of a nature that prevents attacks on the reinforcement.

The present invention is particularly advantageous in connection withpipe installations in which the reinforced flexible tubular pipe is, asfeatured in claim 11, the cleaning and maintaining fluid or gas suppliedto the lumen has a density comprised within the range of from 0.9 and1.1 times the density of the sea water in which the pipe is used.

Moreover, the reinforced flexible tubular pipe is convenientlyconstructed in accordance with the features of claim 14 in that itcomprises a plurality of reinforced flexible tubular pipes that extendbetween an installation arranged on the seabed and to a surface vesselor a platform at sea level.

Finally, claims 12 and 13 feature further convenient embodiments of theinvention.

BRIEF DESCRIPTION OF DRAWINGS

The invention will now be explained in further detail with reference tothe drawings, wherein

FIG. 1 is a perspective sketch illustrating the construction of acommonly known tubular pipe;

FIG. 2 is an explanatory sketch illustrating the principles of a priorart construction in the form of a section through a tubular pipeaccording to the invention;

FIG. 3 is an explanatory sketch corresponding to FIG. 2, depicting,however, a first embodiment of the invention;

FIG. 4A is an explanatory sketch corresponding to FIG. 3, wherein,however, an alternative embodiment of the invention is shown;

FIG. 4B is an explanatory sketch corresponding to FIG. 4A with theaddition of blocking valves;

FIG. 5 is a sectional view of a connecting means according to theinvention;

FIG. 6 is a sectional view of an end coupling element according to theinvention;

FIG. 7 is an explanatory sketch showing an installation comprising atubular pipe in accordance with the invention.

Accordingly, FIG. 1 shows a sketch of a segment of a flexible tubularpipe of commonly known type, which tubular pipe is often used as riserbetween installations on the seabed and an installation located at sealevel, such as a vessel or a platform. For instance, this could be inconnection with the exploitation of oil and/or gases or transport. Thetubular pipe can also be used as transport line between twoinstallations that are both located close to sea level, close to theseabed or relatively deep below sea level.

Such tubular pipes are known today in a wide variety of configurations,and thus FIG. 1 serves only to illustrate, the present invention alsobeing useful in connection with reinforced flexible tubular pipes havingother configurations.

As will appear from FIG. 1, these tubular pipes consist of an innerliner 3 that encloses a carcass 1 constituted by a metal band 2 which iscoiled so as to form an inner pipe, and wherein the metal band 2 is,during coiling, configured with flaps that engage with each otherwhereby they are caused to lock the individual windings in the coiledband 2 to each other in such a manner that the carcass 1 can be flexedout of its longitudinal direction. The inner carcass 1 thus not being initself impermeable, the enclosing liner 3 serves to completely orpartially prevent fluid or gas from flowing from the pipe interior andout.

Obviously, the liner 3 can be a more or less integral part of theabove-mentioned carcass, albeit shown herein as a separate unit.

Exteriorly of the liner 3 and conventionally, one or more layers ofreinforcing profiles 5,6 are coiled that form windings with very littlepitch compared to the longitudinal direction of the tubular pipe. Thus,these windings form a high degree of resistance against the liner 3bursting due to elevated pressure on the tubular pipe inside which meansthat the reinforcement formed by these profiles is often designated apressure reinforcement 4. As will appear from the figure, those profiles5,6 that constitute the pressure reinforcement 4 may be C-shapedprofiles, which profiles have such orientation that two layers ofwindings coiled around the liner 3 in the same direction engage in eachother. However, other profile types, eg Z-shaped and T-shaped profiletypes, are used for the same purpose.

At least some of the prior art tubular pipes are, exteriorly of thepressure reinforcement, provided with a further reinforcement consistingof one or more layers of profiles 7,8 that are most often coiled with asubstantially larger pitch than the above-mentioned pressurereinforcement profiles 5,6, whereby they are able to effectively absorbthe tensile forces in the longitudinal direction of the pipe which mayoccur during laying or operation of the tubular pipe. Therefore thisouter reinforcement is often designated tensile reinforcement.

In order to ensure that the tubular pipe is flexible and can be bentrelative to the longitudinal direction of the tubular pipe, theindividual reinforcing profiles 5,6,7,8 are arranged such that there isplay between the coils thereof. In combination these plays form a lumen10 between the reinforcing profiles 5,6,7 and 8 that allows fluid or gasto flow along the longitudinal direction of the tubular pipe.

Between the above-mentioned reinforcing profiles 5,6,7 and 8, relativelythin layers can be arranged of a material that serves ia to preventtearing between abutting profiles when the pipes are bent.

Obviously the above-described composition of profiles serves merely toexemplify a construction of such reinforced flexible tubular pipe andmany variations can be made on the basis of this fundamental principle.

Generally, however, the exterior of the reinforcing layer that comprisessaid lumen 10 and the reinforcing profiles 5,6,7,8 is provided with anouter jacket 9 that can be configured in a wide variety of wayscomprising, however, at least a material layer, preferably of plastics,which serves as a barrier against fluids flowing freely from thesurroundings of the tubular pipe and into the free volume 10 between thereinforcing profiles 5,6,7 and 8.

Operating conditions in which such pipes function are demanding and itis not possible to achieve full guarantee against small amounts offluids in the form of fluid or gas from the surroundings of the tubularpipe diffusing into the lumen 10 and thus is caused to be in contactwith the reinforcing profiles 5,6,7 and 8. In certain cases this meansthat from the outside of the tubular pipe water diffuses into the lumen10 and that simultaneously ia water, CO₂ and H₂S diffuse into the lumenfrom the tubular pipe interior into the lumen 10 which may give rise toan undesired decomposition of the reinforcing profiles 5,6,7 and 8 withan ensuing substantial reduction in the longevity of the tubular pipe.The accumulation of pressure due to the formation of gas in thereinforcing layer will also in certain cases result in the outer jacketof the pipe bursting.

FIG. 2 is an explanatory sketch of the prior art whereas FIGS. 3 and 4illustrate two alternative embodiments in accordance with the presentinvention. Exclusively for the sake of understanding, these figuresinclude a depiction of the inner liner 3, the outer coating 9 and thelumen therebetween and which contains not shown reinforcing profiles.

Thus, FIG. 2 will show that a flow path 11 is provided that extends fromits inlet opening that debouches into the lumen 10, and out through theouter coating 9, wherein said flow path 11 is provided with a one-wayvalve 15 which is so configured that it allows unimpeded flow provided apositive difference in pressure prevails between the reinforcing layerand the surroundings.

In an operative situation it is hereby possible to have a flow of fluidor accumulated gas from the lumen 10 and out on the outside of the tubewhen the pressure in the lumen exceeds the ambient pressure.

In the first embodiment of the invention the flow path, as shown in FIG.3, debouches in the pipe interior 14. As shown in the figure, the flowpath includes a pump 12 that is able to actively pump fluid from thelumen to the pipe interior.

Now, FIG. 4A shows the second embodiment of the invention wherein,instead of the pump shown in FIG. 3, a valve 15 is arranged which is ofthe one-way type. The one-way valve shown in FIG. 4A can, in a preferredembodiment shown in FIG. 4B, be configured with [no shown] blockingvalve means 40, 50 for closing the valve completely to flow from bothsides in response to given information, thereby further contributing toavoid occurrence of undesired flow of fluids or gases from the pipeinterior and into the lumen through the flow path 11. Correspondingmeans can also be provided in combination with the pump shown in FIG. 3with the result that also in this embodiment, it is ensured to a higherdegree that backflow of fluids from the surroundings of the tubular pipeand into the lumen 10 is avoided, and such means can optionally be usedboth upstream and downstream of the one-way valve or the pump with aview to servicing same in practice without ensuing risk of leak form thelumen and from the pipe interior.

Obviously, alternative embodiments and other combinations than the twosuggested in FIGS. 3 and 4 are thinkable. In practice tubular pipes withthe construction in accordance with the principles shown in FIG. 1 aremanufactured in final lengths, the pipes in question having considerablediameters and bulks that are handled only with difficulty when verylong. Therefor coupling elements are often used for coupling one or morepipes of the type shown in FIG. 1, whereby tubular pipes of desiredlengths can be produced, the lengths of which exceed the length of asingle integral tubular pipe.

Thus, FIG. 5 is a sectional view illustrating a part of a connectingelement having a pipe mounted therein which is of the type shown in FIG.1. Thus, this coupling element has a mounting flange 16 with an abutmentface 19 and a holding element 17 and 21 for securing a tubular pipe thatconsists of an inner carcass 1, an inner liner 3, reinforcing profiles5,6,7 and 8 which are arranged in the lumen 10, and an outer coating 9.

In a known manner means are provided that are intended to secure thetubular pipe in the coupling element.

As will appear and in accordance with the invention, a flow passage 18is provided that extends from the lumen 10 and to the abutment face 19of the mounting flange which means that this flow passage 18 can bearranged opposite a corresponding flow passage on another connectingelement or another construction thereby enabling emptying of the lumen10 via this flow passage 18.

Now FIG. 6 shows an alternative embodiment of a coupling elementaccording to the invention in the form of an end coupling element, themost significant difference being, in this context, that the flowpassage 20 leads to the side of the coupling element which enablesdirect coupling of a valve thereto in the same manner as is shown inprinciple in FIG. 2, 3 and 4.

The end coupling element according to FIG. 6 is, according to apreferred embodiment of the invention, provided with a duct 20 for theintroduction of fluids for maintenance. This means that, at the upperend of the pipe, fluids or gases can be introduced which willsubsequently flow in the lumen of the pipe and downwards andconsequently effectively treat the reinforcing profiles and optionallyother components of the pipe.

According to a further preferred embodiment of the invention, a flowpassage of the type shown in one of the above-described FIGS. 3 to 4 isprovided at the lowermost end of the pipe in such a manner that themaintenance fluids can be discharged thereby.

Now FIG. 7 is an explanatory sketch illustrating an end coupling element30 for securing a tubular pipe 32 fra eg a vessel 31 or a platformwhereby the tubular pipe 32 can be used as riser and is more or lessfreely suspended from the vessel 31 or the platform and is at thebottom—in a manner known per se—secured to an installation at the seabedby means of an end coupling 33. According to one aspect of the presentinvention, the end coupling element 30 at the vessel 31 or the platformcan be provided with a filling duct as stipulated above for fillingmaintenance fluids into the lumen in the tubular pipe 32, and the endcoupling element 33 at the seabed can be provided with a flow passage asdescribed above in connection with the figures, for discharging fluidsfrom the lumen of the tubular pipe 32.

Obviously the present invention can be exercised in other manners thanthe ones shown above, it being possible to exercise the principles ofthe invention within a very wide framework in connection with pipes,coupling elements and end coupling elements of differing configurationswithout hereby modifying the fundamental functioning of the invention.

What is claimed is:
 1. A reinforced flexible tubular pipe comprising aninner liner that forms a barrier against outflow of a medium that flowsthrough an interior of the pipe, said inner liner being encased by atleast one reinforcing layer containing a plurality of profiles that arecoiled around the inner liner such that the profiles are completely orpartially enclosed by a lumen that allows transport of fluids in thelongitudinal direction of the pipe, an outer jacket disposed outside thereinforcing layer for forming a barrier against free inflow of fluids,gases, or both from surroundings of the pipe to the reinforcing layer,and at least one flow path for conveying fluid or gas away from saidlumen to the interior of the pipe for transport of the conveyed fluid orgas with the medium that flows through the pipe interior.
 2. Areinforced flexible pipe according to claim 1, comprising means disposedin the flow path to prevent flow of transported fluid into the lumen. 3.A reinforced flexible tubular pipe according to claim 2, wherein the atleast one flow path comprises at least two blocking valves that are,flow-wise, disposed on respective first and second sides of the means.4. A reinforced flexible tubular pipe according to claim 2, wherein themeans comprises a valve that allows flow only when a negative differenceof pressure prevails between the pipe interior and the lumen.
 5. Areinforced flexible tubular pipe according to claim 2, wherein the meanscomprise a pump that forces flow of fluid from the lumen and into thepipe interior.
 6. A reinforced tubular pipe according to claim 5,wherein the pump comprises a passageway or a by-pass valve that enablesthe pump to always flow provided a negative difference in pressureprevails between the pipe interior and the lumen.
 7. A reinforcedflexible tubular pipe according to claim 1, wherein the at least oneflow path comprises a safety valve.
 8. A reinforced flexible tubularpipe according to claim 1, comprising a coupling element for securingthe reinforced flexible tubular pipe on another construction or toanother tubular pipe, wherein the at least one flow path completely orpartially extends into the coupling element.
 9. An apparatus comprisingfirst and second reinforced flexible tubular pipes according to claim 1,said first and second tubular pipes being connected by a connectingelement, wherein the connecting element is provided with ducts thatallow fluid and gas within the first reinforced flexible tubular pipe toflow through the connecting element into the reinforcing layer in thesecond reinforced flexible tubular pipe.
 10. A reinforced flexibletubular pipe according to claim 1, comprising at least one further flowpath disposed to supply a fluid or gas for cleaning and maintenance tothe lumen.
 11. A method for transporting fluids or gases comprising (a)providing the reinforced flexible tubular pipe according to claim 10 ata depth beneath the sea; and (b) supplying a fluid or gas to the lumenfor cleaning and maintenance thereof, wherein the fluid or gas forcleaning and maintenance supplied to the lumen has a density within arange of from 0.9 to 1.1 times a density of the seawater at sea depth.12. A reinforced tubular pipe according to claim 10, wherein the flowpath for supplying the fluid or gas for cleaning or maintenance isdisposed at an upper end of the reinforced flexible tubular pipe.
 13. Areinforced flexible tubular pipe according to claim 1, wherein thereinforced flexible tubular pipe comprises an upper and a lower end withthe lower end being disposed below the upper end, and wherein the atleast one flow path for conveying fluid or gas away from the reinforcinglayer is disposed at the lower end of the reinforced flexible tubularpipe.
 14. An apparatus comprising a plurality of reinforced flexibletubular pipes according to claim
 1. 15. A method for transporting afluid or gas between an installation at a seabed and a surface vessel,said method comprising (a) providing a pipe installation comprising aplurality of pipes according to claim 1, said pipe installationextending between, the seabed and the surface vessel; and (b)transporting the fluid or gas between the installation at the seabed andthe surface vessel through the pipe installation.